# Is there a way of approximating e^-x for large x

by Chain
Tags: approximating
 HW Helper P: 2,264 Are you talking about Gauss–Laguerre quadrature? $$\int_0^\infty f(x) e^{-x} \mathop{\text{dx}}\sim \sum_{i=1}^n w_i f(x_i)$$ where xi are zeros of a Laguerre polynomial and $$w_i=\frac{x_i}{(n+1)^2[L_{n+1}(x_i)]^2}$$